1. Field of Invention
The present invention relates to a gas-delivering device installed within a semiconductor reaction chamber. More particularly, the present invention relates to a gas-delivering device that can be used for balancing gas flow rate inside the reaction chamber according to the conditions within the chamber.
2. Description of Related Art
As IC fabrication is now in the sub-micron range and processing diameter of a silicon wafer continues to increase, how to establish a highly uniform plasma atmosphere in a reaction chamber is of growing importance. Ultimate uniformity of a processed wafer and microloading effect are closely related to the uniformity of plasma within a reaction chamber. The so-called microloading effect refers to the difference in etching rate or depositing rate in an etching operation or thin film production that results from a variation of exposed area due to a specific pattern distribution. Consequently, in semiconductor manufacturing operations such as etching or layer deposition, a system capable of providing a uniform supply of gases source is very important.
FIG. 1 is a cross-sectional view showing the layout of a conventional reaction chamber. As shown in FIG. 1, a gas-delivering panel 110 and a negative electrode are located inside a reaction chamber 100. The gas-delivering panel 110 can be fixed to the ceiling of the reaction chamber 100, while a wafer 120 can be placed on top of the negative electrode. The reaction chamber 100 has an exhaust outlet connected to a pump via a throttle valve. When the pump is in operation, gases within the chamber 100 are sucked out to maintain a high degree of vacuum within the reaction chamber 100. Furthermore, when a thin film deposition or an etching operation is performed, gaseous reactants can flow into the reaction chamber 100 through the gas-delivering panel 110 so that appropriate reactions with the wafer 120 can take place within the chamber. Structural details of the gas-delivering panel can be seen in FIGS. 2A and 2B.
FIGS. 2A and 2B are the top views of two types of conventional gas-delivering panel installed on the ceiling of the reaction chamber as shown in FIG. 1. As shown in FIGS. 2A and 2B, the gas-delivering panels 110 have a circular plate-like structure with a plurality of symmetrically positioned holes 112. Here, the symmetry point is the center of the circular plate-like structure. Because the gas-delivering panel 110 is installed on the ceiling of the reaction chamber 100, gases coming down from the holes 112 are able to react with the wafer 120 (FIG. 1) in etching or film growing operations.
Since the gas-delivering panel 110 is fixed in position on the ceiling of the reaction chamber 100, gases diffusing down through the symmetrical holes 112 ought to be able to form a uniform layer of gas above the wafer. However, in practice, gas flow within the chamber is highly asymmetrical due to the asymmetrical nature of the fixtures within the reaction chamber 100. Therefore, non-uniformity of gas flow or even a turbulent gas flow is the norm, especially when the pump is operating to create a vacuum. Under such circumstances, uniformity of wafer deposition or etching is affected and microloading effect intensifies. Consequently, product yield is lower and die quality deteriorates.
In light of the foregoing, there is a need to provide a gas-delivering panel structure capable of smoothing the flow of gaseous reactants within the reaction chamber.
Accordingly, the present invention is to provide a gas-delivering device capable of balancing the gas flow rate directed towards a wafer surface according to the actual conditions within the chamber. Hence, a uniform flow of gaseous reactants is delivered to a wafer surface for carrying out various types of reactions.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a gas-delivering device for a reaction chamber. The gas-delivering device comprises a panel that includes holes drilled in it such that a greater number of holes is formed in places where gas flow is weak. Since the holes are distributed asymmetrically around the gas-delivering panel, more gases can be diverted to chamber areas where the gas flow rate is deficient. Therefore, gaseous reactants can be more uniformly spread inside the reaction chamber.
Actual position of the asymmetrically placed holes depends very much on the actual gas flow conditions within the reaction chamber. In general, asymmetrical hole patterns are formed near places where the gas flow rate is small or air pressure is low. Consequently, a larger volume of gas can flow into these gas deficient areas, thereby homogenizing the gaseous distribution inside the chamber.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.